My newly bought iPhone 16 Pro not charging even when plug

You need to contact Apple Support, then.

Best way: 

• Install the Apple Support app on your iPhone or iPad - you can contact support directly from the app, and the tech will have (with your permission) access to diagnostic data on your device

Other options:

• • Click on “Support” at the top or bottom of this page
  • Go to Contact Official Apple Support

(Note that both of the above have options to receive a callback or chat)

• • Call Apple Support; the phone numbers are in this link→Contact Apple for support and service - Apple Support
  • Make a Genius Bar appointment at an Apple Store→Genius Bar Reservation and Apple Support Options - Apple
  • Find an Apple store or Apple partner service provider→Find Locations

Have you tried a different power source (at least 10 watts, 20 watts is optimal) and a different cable?